Drug sensitivity in herding breeds

What is MDR1? 

Multi-drug resistance 1, or MDR1, is a gene mutation found in many herding breeds.  This mutation causes toxic levels of certain drugs to build up in the brain; which leads to severe neurological problems, such as seizures and death.  It is estimated that around 75% of all collies have the MDR1 mutation, so all collie owners should be aware of which drugs are potentially harmful to their dogs.  If you are concerned that your collie, or herding breed, may have this mutation, there is now a simple, inexpensive DNA test offered.  For around $70, and with just a quick cheek swab, you can have your dog tested.

How does a dog end up with this mutation?  Each collie receives one allele, or gene, from each of it's parents.  Dogs that receive a "normal" MDR1 gene from each parent are +/+ (homozygous normal) or normal/normal.  All offspring from these parents will be clear of the MDR1 mutation, and will not be sensitive to the drugs listed below.

Dogs that receive a "normal" gene from one parent, and a "mutant" gene from the other parent are +/- (heterozygous).  While they are considered to be only carriers of the mutation, studies have found that they may also be sensitive to certain drugs.  These dogs will pass along the mutant gene to half of their offspring.

Dogs that receive a "mutant" gene from both of their parents are -/- or mutant/mutant. (homozygous mutant)  Dogs that are mutant/mutant are very sensitive to certain drugs, such as Ivermectin, and will pass on the mutation to all of their offspring.  According to the Collie Health Foundation and other leading researchers, the low dose of Ivermectin found in monthly heartworm medications will not cause a reaction.  However, many collie owners and breeders still choose to avoid use of any products containing Ivermectin, preferring to exercise caution instead.

Because of the need for caution, if your dog tests mutant/mutant or normal/mutant, you should make sure that any veterinarian treating your dog is aware of the risks of using certain drugs.  You will also want to make sure your dog does not ingest horse feces, because horses are treated with large quantities of Ivermectin and the drug is eliminated from their bodies in their feces.

Herding breeds at risk:
Australian Shepherds
Collies (rough and smooth)
English Shepherds
German Shepherds
Long-haired Whippets
McNabbs
Shetland Sheepdogs
Silken Windhounds
and any mixed-breeds with any of these breeds in their ancestry.

Dogs with the MDR1 Gene Defect should avoid the following drugs:

 Class A

Ivermectin substances (antiparasitics, such as Diapec, Ecomectin, Equimax, Ivomec, Noromectin, Paramectine, Qualimec, Sumex, Virbamec)

Doramectine substances (antiparasitics such as Dectomax)

Loperamide substances (antidiarrheal, such as Imodium)

Moxidectine substances (antiparasitcs such as Cydectin, Equest, Flagyl)

Class B (used only under CLOSE supervision of veterinarian):

Cytostatics (chemotherapy)

Immunosuppressive (Cyclosporine A)

Heart glycosides (Digoxine, Methldigoxine)

Opiods (Morphium)

Antiarrthymics (Verapamil, Diltiazem, Chinidine)

Antiemetics (Ondansetron, Domperidon, Metoclopramide)

Antibiotics (Sparfloxacin, Grepafloxacin, Erythromycin)

Antihistamin (Ebastin)

Glucocortoid (Dexamethason)

Acepromazine (tranquilizer and pre-anesthetic agent)

Butorphanol (analgesic and pre-anesthetic agent)

Etopside

Mitoxantrone

Ondansetron

Paclitaxel

Rifampicin

Class C (used in permitted application form and dose):

Selamectin

Milbemax

Advocate

When choosing a veterinarian for your dog, please make sure they are educated on the MDR1 mutation and know which drugs pose a risk to your dog.  You should also keep a list when you are traveling with your dog, because not every veterinarian is aware of these potentially harmful drugs and in some emergency situations time is limited.

For herding breeds, there is an old saying - Got white feet?  Be careful before you treat!